Quote Originally Posted by DDT
Perhaps you also know why a land mile is shorter than a nauticle mile?
Because Nautical and Geographic distances were based on astronomical measurements (made with a sextant) since there was no easy way to measure a distance between to points, or a number of paces, etc as there is on land. Actually, they are remarkably close considering how differently they were arrived at!


http://www.fishsa.com/boatngsn.php
On the ocean, distances are calculated slightly differently than on land, hence Nautical phrases are applied as opposed to land or Statute terminology.

Nautical Mile (nmi): A unit of distance used in navigation and based on the length of one minute of arc taken along a great circle. This is also sometimes referred to as the International Nautical Mile or an International Air Mile.

Please Note the following:

* Because the Earth is not a perfect sphere, various values have been assigned to the nautical mile. The value 1852 meters (6076.1 ft.) has been adopted internationally.

* The nautical mile is frequently confused with the geographical mile, which is equal to 1 min of arc on the Earth's equator (6087.15 ft.).

http://hypertextbook.com/physics/fou...ystem-english/
One mile was the distance of a thousand paces: in Latin, mille passus. A pace being 5 feet gives a mile of roughly 5000 feet. The current length is defined at 5280 feet. Since this was a legal definition it is often also known as a statute mile. Statute being another word for law. From Webster's 1913: "The distance called a mile varies greatly in different countries. Its length in yards is ...

* Austria, 8,297 yards
* Brunswick, 11,816 yards
* England and the United States, 1,760 yards
* Hungary, 9,139 yards
* Italy, 2,025 yards
* Netherlands, 1,094 yards
* Norway, 12,182 yards
* Poland, 8,100 yards
* Prussia, 8,238 yards
* Spain, 1,552 yards
* Sweden, 11,660 yards
* Switzerland, 8,548 yards


Also, I got to thinking when I was looking up these references and doublechecked my "knots" explanation - which was essentially correct. If you're interested, here is a much fuller explanation which also ties it into nautical miles and explains how it was calculated.
http://www.physlink.com/Education/AskExperts/ae400.cfm